1. Field of the Invention
The present invention relates to a wiper blade, in particular for motor vehicles, having a superstructure linked to a wiping element which is reinforced by a longitudinal pressure distributing profile provided with an air deflecting device.
2. Background of the Prior Art
Air deflecting devices which are attached to one of the elements of the superstructure of a wiper blade are well known in the prior art. By way of example, the French Patent Publication No. 2,513,953, wherein the air deflecting device is attached to the main bridge of the superstructure of the wiper blade, and the German (DE) Patent Publication No. 23 46 100, wherein the air deflecting device is attached to the secondary bridges or yokes of the superstructure of the wiper blade, may be mentioned.
Indeed the air deflecting device according to the present invention is not attached to one of the elements of the superstructure of the wiper blade, but is attached to the flexor or longitudinal pressure distributing profile with which the wiping element of any wiper blade is provided.
An air deflecting device attached to (or being an integral part of) the flexor or longitudinal pressure distributing profile of the wiper blade is known through the French Patent Publication No. 2,513,952. However, the different forms of an air deflecting device disclosed in this French patent publication solve the air deflecting problem only very imperfectly, just as, by the way, the solutions proposed in the French Patent Publication No. 2,513,953 and in the German (DE) Patent Publication No. 23 46 100.
The problem to be solved is: when the wiper blades of a motor vehicle are working and when said vehicle moves at a relatively high speed, the wiper blades have a tendency to lift, i.e. to move away from the windshield under the action of the air which flows along the windshield, thus rendering the visibility worse and worse as the speed of the vehicle increases.
As a matter of fact, depending on the speed of the vehicle, three stages may be distinguished in the thus defined phenomenon. During the first stage slight wiping defects slowly appear on the windshield. These defects, in spite of the fact that they are not negligible, still permit driving of the vehicle without taking too important of a risk. During the second stage these wiping defects become more and more important and it becomes dangerous to drive the vehicle. The third stage corresponds to the moment where the wiping element lifts or moves away from the windshield. At this moment there is no longer any visibility and the driver is forced to slow down the speed of the vehicle.
Tests performed on vehicles placed in a wind-tunnel have shown that the starting point of each of the three above-mentioned stages can be displaced towards higher vehicle speeds, for example in using air deflecting devices attached to one or the other element of the wiper blade.
These tests have also shown that the studied phenomenon depends on certain parameters which are not directly linked to the type of wiper blade or to the type of air deflecting device used. One can mention the influence of the form and of the inclination of the windshield of the vehicle.
In taking into consideration only the air deflecting devices attached to the flexor or longitudinal pressure distributing profile, tests in the wind-tunnel have shown that, for guaranteeing a maximum efficiency, an air deflecting device of this type must comply with the following conditions:
1. The properly so called deflector (as opposed to the attachment means) must be located at a non-negligible distance from the wiping element of the wiper blade.
2. It must be possible for the air to circulate between the properly so called deflector on the one side and the assembly wiping element/longitudinal pressure distributing profile on the other side, or in other words, there must be a longitudinal opening between the properly so called deflector and the longitudinal pressure distributing profile of the wiping element.
3. The ratio between (a) the distance between the properly so called deflector and the wiping element and (b) the distance between the lower edge of the properly so called deflector and the surface to be wiped is substantially equal to ten.
In none of the embodiments disclosed in the three above mentioned patent publications were these three conditions complied with and the tests have shown that in such a case the positive effect obtained is relatively small. Furthermore, if the mentioned conditions are not complied with and if other parameters have a negative effect, the total effect may be negative.